Self cleaning, perforated plate for oscillating sieve

ABSTRACT

A screen panel for vibratory screening machines can consist of at least one cast, injection-molded or vulcanized perforated plate of elastically flexible material, such as plastic or rubber. It has a multitude of screen openings (5) and crosspieces (2, 3, 4) surrounding them which are interconnected forming one piece and thus the perforated plate. A self-cleaning effect can be achieved with such a perforated plate in the area of each individual screen opening (5) by means of a relative movement of the edges of the screen openings in order to extend the self-cleaning effect to as large an area as possible of each individual screen opening (5). For this purpose, at least two of the crosspieces (2-4) surrounding the individual screen openings (5) have a differing bending resistance by means of differing cross-sections and/or reinforcements (8).

BACKGROUND OF THE INVENTION

The invention refers to a screen panel for a vibratory screeningmachine.

Such a screen panel consists of at least one cast, injection-molded orvulcanized perforated panel of elastically flexible material, such asplastic or rubber, with a multitude of screen openings and crosspiecessurrounding them which are connected with each other as one piece andform perforated panels.

Such screen panels are predominantly used for the classification of bulkmaterials. In order to avoid an obstruction of the screen openings,particularly by means of near-size material, it is known to takemeasures towards a self-cleaning effect for such screen panels. As arule, the screen openings are designed with a conic expansion in thedirection of the flow of the material to be screened so that wedged-innear-size material can be moved by being carried along by the materialto be screened in its direction of flow. However, there exists also bulkmaterial due to which the screen openings get choked up with mud and, inthis instance, the individual particles depositing in the screenopenings are by far smaller than the respective near-size material whichmakes the conicity of the screen openings ineffective against thechoking-up with mud.

A known screen panel of the kind mentioned in the introduction isdescribed in the German Disclosure Publication No. 27 01 307. In thisinstance, the self-cleaning effect is improved by the fact that elastictongues are formed in the individual screen openings capable of theirown vibration. Two screen holes are always connected with each other bya slot in this case and the strip formed in this way, which is onlyrigidly connected with the crosspieces on one end, has a higherelasticity in comparison with the edges of the screen openings andcarries out relative movements. However, the self-cleaning effect causedin this fashion is essentially limited to the area of the freelyvibrating ends of the tongues since, towards the connecting point withthe crosspieces, the relative movement of the tongues is more and morereduced towards the edges of the screen openings.

A known screen panel is also described in the German Pat. No. 965,546.In this case, the screen panel consists of elastic, strip-shapedelements which have also strip-shaped tongues attached laterally intransverse direction which extend in a determined arrangement to theadjacent strip-shaped element and surround the screen openings. Thesetongues have no connection with the respective adjacent crosspieces and,therefore, can effect their own vibration and thus a relative movementat least in the area of their free ends towards the continuouscrosspieces whereby a self-cleaning effect is obtained which isessentially limited to the area of the ends of the tongues in this caseas well. Owing to the relative movements of the vibrating strips incomparison with the crosspieces to which they are attached, specialdifficulties are encountered, on the one hand, with regard to durabilityand, on the other hand, with respect to the trueness of the holes of thescreen openings. For this reason, the tongues, being additionallycapable of vibrating, are, at least partially, provided with areinforcement and, furthermore, project downward beyond the actualsectional height in order to achieve a sufficient trueness of the meshor hole with the larger movement in comparison with the more rigidcrosspieces.

Wire screen panels have already been known for a long time in which theindividual screen openings are surrounded by screen wires which consistof steel. In this case, relative movements of the individual screenwires are produced by means of a differing configuration of the screenwires next to each other or by means of differing wire thicknesses whichcause a cleaning effect. The individual screen wires of differingbending resistance must be adjusted to each other in a special mannerand fastened to a joint support frame. Even though such wire screenpanels have been in use for already more than twenty years, they havenot represented a suggestion so far towards the improvement of theself-cleaning effect also of screen panels of the kind mentioned in theintroduction with perforated panels of elastically flexible material.(Obering. Kurt Wolff: "Screen panels and their use" in"Aufbereitungstechnik", Year 1 (1960), Issue 11, Pages 457-473 and Issue12, Pages 501-508).

SUMMARY OF THE INVENTION

Proceeding from a screen panel of the above described kind, theinvention is now based on the task of achieving the self-cleaning effectin the area of each individual screen opening by means of a relativemovement of the edges of the screen openings in order to expand thus theself-cleaning effect to as large an area as possible of each individualscreen opening. This task is accomplished in the case of a screen panelof the mentioned kind by the fact that at least two of the crosspiecessurrounding each of the individual screen openings have differingbending resistances as a result of their differing cross-sections and/orreinforcements.

The special advantage of a screen panel according to the invention liesin the fact that the continuous crosspieces of the perforated paneldeform towards each other during operation whereby the individual screenopenings can be distorted within determinable limits. The change inshape covers then the entire area of each screen opening, particularlythen when the crosspieces of differing bending resistance are located atopposite sides of the screen openings. In order to be able to utilizethe advantages of the relative movement of the crosspieces of differingbending resistance not only for slot-shaped screen openings but also forrectangular, square or round screen openings, it is advantageous tolimit the screen openings by means of extensions attached to thecrosspieces whereby these extensions follow the relative movement of thecrosspieces with which they are connected. Additionally, theseextensions can perform a vibration of their own in order to increase thecleaning effect.

The differing bending resistance of the two crosspieces assigned to eachscreen opening can be produced, as far as the difference incross-section in concerned, by means of a difference in thecross-sectional shape as well as by means of a difference in thecross-sectional size. Additionally, the differing bending resistance ofthe two crosspieces can also be influenced by providing armoring or areinforcement. However, in principle, the differing cross-sectionalshapes and sizes are not required when these crosspieces are providedwith a reinforcement. This reinforcement of the crosspieces of differingbending resistance can be different but, in a preferred design, onecrosspiece will be alternately used with reinforcement and one without.

A parallel arrangement of the crosspieces of differing bendingresistance is expedient. In this way, it is possible to form regularlyarranged, equally large screen openings, particularly screen slots. Theparallel arrangement of these crosspieces has the effect that theindividual screen openings have a different vibration behavior on theiredges which are located opposite each other. This is independent of howthe screen openings are designed or formed in an overall manner which isespecially advantageous when--as already mentioned--the screen openingsare also delineated by the extensions attached in cross direction to thecrosspieces. The screen openings are, furthermore, delineated by meansof crosspieces on the edges or by means of crosspieces intersecting thecrosspieces of differing bending resistance; these last mentionedcrosspieces produce the interconnection of the screen panel. Allcrosspieces are connected with each other, forming one piece, owing tothe cast, injection-molded or vulcanized design of the perforated plate.

In the case of a perforated plate which is supported all around, agreater vibrational amplitude develops towards the center of theperforated plate than at the supported edges owing to the diaphragmaction. In order to achieve a sufficient self-cleaning effect in thisinstance at the edges as well, it is advantageous to design theinterconnections of the parallel and crossing crosspieces less rigidlyby increasing the distance either of the parallel and crossingcrosspieces or only of the crossing crosspiece towards the edges of theplate. In this fashion, a greater vibrational amplitude is obtained alsoin the area of the edges.

The vibrational behavior and/or the wear of the crosspieces of differingbending resistance can also be influenced by varying the level withwhich they project above the upper side of the perforated plate. On theone hand, the more flexible crosspieces may have an upward projectionwhereby the material to be screened which falls on the projectingcrosspieces increases their vibrations and thus the self-cleaningeffect. On the other hand, the more rigid crosspieces may also projectupward beyond the upper side of the perforated plate. This measure istaken in order to carry the coarser material to be screened with theprojection of the more rigid crosspieces; in this manner, the moreelastic areas are relieved of the load and are not so much endangered bywear.

In addition to the self-cleaning effect achieved by the differingbending resistance of the crosspieces, the conic expansion of the screenopenings in the direction of the flow can also be provided for a screenpanel according to the invention in order to obtain a release ofnear-size particles in the customary manner.

BRIEF DESCRIPTION OF THE DRAWING

The invention is still further explained by means of exemplifiedembodiments on the basis of the drawing. There are shown:

FIG. 1 a perspective, sectional top view of a perforated plate for ascreen panel according to the invention;

FIG. 2 a cross-section through another design of a perforated plate fora screen panel according to the invention;

FIG. 3 a partial cross-section through another design of a perforatedplate for a screen panel according to the invention;

FIG. 4 a partial cross-section in an enlarged representation through afourth design of a perforated plate for a screen panel according to theinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows the basic structure of a perforated plate for a screenpanel which is intended for use in vibratory screens for theclassification of bulk material. The perforated plate consists of anelastically flexible material, such as plastic or rubber. It is cast,injection-molded or vulcanized in one piece using this material.

The perforated plate has boundary members 1 along the edges thereofbetween which longitudinal crosspieces 1 and 3 and transversely arrangedcrosspieces 4 extend. These crosspieces are hereinafter calledlongitudinal crosspieces and transverse crosspieces although they canrun, in principle, also diagonally towards each other as well as towardsthe boundary members 1 along the edges. Also, the design and function ofthe longitudinal and transverse crosspieces can be interchanged whichmay apply to the entire perforated plate as well as to partial areasthereof.

The boundary members along the edges serve to support or secure theperforated plate and have a larger cross-section in comparison with thelongitudinal crosspieces 2 and 3 as well as the transverse crosspieces4. Furthermore, the cross-sections or the longitudinal crosspieces 2 andof the longitudinal crosspieces 3 differ as well. The cross-sectionalshapes of the longitudinal crosspieces 2 and of the longitudinalcrosspieces 3 are actually identical to one another since thelongitudinal crosspieces 2 and the longitudinal crosspieces 3 havesquare or rectangular cross-sections but there is a difference in thesize of the cross-sections of the crosspieces 2 and 3. The longitudinalcrosspieces 2 have a larger cross-section than the longitudinalcrosspieces 3 and have, therefore, a higher bending resistance than thelongitudinal crosspieces 3 because of their larger cross-section sincethe perforated plate, being produced of the same material, is of onepiece. For this reason, they have a different vibrational behavior thanthe more elastic longitudinal crosspieces 3 so that the longitudinalcrosspieces 2 perform a relative movement towards the longitudinalcrosspieces 3 during operation.

Since the longitudinal crosspieces 2 and 3 enclose, between themselves,screen openings 5 located in a row one behind the other, i.e. delineatethese screen openings 5 on opposite sides, the basic shape of the screenopenings 5 is deformed during operation owing to the relative movementbetween the crosspieces 2 and 3. The screen openings 5 can be designedas continuous oblong slots between the transverse crosspieces 4 but thetransverse crosspieces 4 can also be entirely eliminated so that theslot-shaped screen openings 5 extend only between the opposite boundarymembers 1 along the edges of the perforated plate. The number of thetransverse crosspieces 4 which support the interconnection of theperforated plate depends of course also on the size of the perforatedplate. However, it is largely independent of the length of the screenopenings because the screen openings 5 can also be defined by tongues orextensions 6 on the longitudinal crosspieces 2 and 3. In the exemplifiedembodiment, two such tongues or crosspiece extensions 6 are attached todifferent crosspieces 2, 3 and are always opposite each other, but astaggered arrangement of the extensions 6 on the crosspieces 2, 3 isalso possible. A slot 7 is left between the opposite end faces of thecrosspiece extensions 6 so that the crosspiece extensions 6 which areconnected with crosspieces having a different vibrational behavior, canmove more freely relative to each other. Such a slot 7 at the forwardend face of the respective crosspiece extensions 6 is also then to beprovided when the crosspiece extension 6 extends to the respectiveopposite longitudinal crosspiece. The crosspiece extensions 6 make itpossible to divide each opening between the crosspieces 2, 3 ofdiffering bending resistance in such a way that screen openings 5 of anyconfiguration can be formed.

As can also be noticed from FIG. 1, the distance "A" of the transversecrosspiece 4 adjacent to the crosspiece 1 at the edge is larger than thedistance "B" between the transverse crosspieces 4 themselves. Thisgreater support distance "A" ensures a higher elasticity of theinterconnection consisting of the crosspieces 2, 3 and 4 in the areatowards that crosspiece 1 at the edge in which the crosspieces 2 and 3of differing bending resistance end. Since the entire perforated platevibrates during operation like a diaphragm and, therefore, thelongitudinal crosspieces 2 and 3 of a differing bending resistanceperform the greatest vibrational amplitude, the area close to theboundary members 1 at the edges is at a disadvantage with its smallervibrational amplitude for which a compensation can be obtained by thegreater elasticity in this area at the edges. So as to produce the sameeffect also in the area at the edges towards those crosspieces 1 at theedges which are in parallel to the longitudinal crosspieces 2 and 3, thedistances of these longitudinal crosspieces 2 and 3 can also be enlargedtowards the respective members 1 along the edges.

Independently of this fact, the crosspieces 2 of a greater bendingresistance must always be arranged in an alternating manner with thecrosspieces 3 of a lesser bending resistance so that, looked at in thedirection of the transverse crosspieces 4, a more resistant longitudinalcrosspiece 2 is always followed by a more elastic longiutdinalcrosspiece 3 and this again by a more resistance longitudinal crosspiece2.

FIG. 2 shows a perforated plate design in which the differing bendingresistance of the longitudinal crosspieces 2 and 3 is not caused bydifferent cross-sectional shapes or sizes but by a reinforcement 8. Inthis instance, the longitudinal crosspieces 2 and 3 have identicalcross-sections and the reinforcement 8 is only embedded in every secondlongitudinal crosspiece 2 looked at in transverse direction while therespective longitudinal crosspieces 3 located in between them have noreinforcement.

FIG. 3 shows the exemplified embodiment of a perforated plate in whichthe more resistant longitudinal crosspieces 2 have attached extensions 9projecting above the upper face 10 of the screen which have the task ofsupporting coarser material to be screened in order to relieve the moreelastic longitudinal crosspieces 3 and transverse crosspieces 4 of highwear. The vibrational behavior can also be influenced by the projectingextensions 9 but it would then be advantageous to provide the projectingextensions 9 on the more elastic longitudinal crosspieces 3.

FIG. 4 illustrates, on the one hand, the possibility of providing themore resistant longitudinal crosspieces 2 with a stronger reinforcementand the more elastic longitudinal crosspieces 3 with a more easilybendable reinforcement 8 in comparison with the reinforcement of themore resistant longitudinal crosspieces 2. Therefore, the differingbending resistance is produced in this design by the cross-sectionalsizes of the longitudinal crosspieces 2 and 3 as well as by thedifferent reinforcement 8. It is expedient to arrange the reinforcement8 in the area of the lower third of the cross-section of thelongitudinal crosspieces 2 and 3.

Furthermore, one can notice in FIG. 4 particularly clearly thewedge-shaped design of the longitudinal crosspieces 2 and 3 which isalso provided for the transverse crosspieces 4 so that the screenopenings 5 get wider in the direction of the flow. This is achieved forthe more resistant longitudinal crosspieces 2 as well as for the moreelastic longitudinal crosspieces 3 and for the transverse crosspieces 4by means of lateral delineating surfaces 11 and 12 of the crosspieces2-4 which converge in the direction of the flow; however, this cannot benoticed in detail from FIG. 4.

FIG. 4 shows still another feature of the crosspiece extensions 6 on thelongitudinal crosspieces 2 and 3. The extensions 6, opposite each other,have end faces 13 diverging in the direction of the flow so that theslot 7 located between them also expands in the direction of the flow ofthe material to be screened. A corresponding inclination of the endfaces 13 of the crosspiece extensions 6 is also then to be provided whenthe crosspiece extensions 6 of the one crosspiece 2, 3 extend to therespective other crosspiece 2, 3; the conicity of the slot 7 is thenformed, on the one hand, by the oblique face 13 of the respectivecrosspiece extension 6 and, on the other hand, by the obliquely arrangedlateral face 11, 12 of the pertinent crosspiece 2, 3.

As is additionally illustrated in FIG. 4, the crosspiece extensions 6can also be tapered towards their free ends, i.e. towards the end face13. This is expediently achieved by lower faces 14 of the crosspieceextensions 6 running in an inclined manner to the upper face 10 of thescreen. The lower faces 14 of the crosspiece extensions 6 can also bedesigned in a curved fashion and the end faces 13 of the crosspieceextensions 6 can make a continuous transition into the lower faces 14 ofthese crosspiece extensions 6.

I claim:
 1. A screen panel for use in a vibrating screening machinecomprising a one piece element which includes a boundary member definingthe outer periphery of said panel, a first plurality of spacedcrosspiece members disposed in parallel relation to one another andextending between portions of said boundary member, a second pluralityof spaced crosspiece members disposed in parallel relation to oneanother and to said first plurality of spaced crosspiece members betweenportions of said boundary member, the crosspiece members in said firstand second pluralities being disposed in alternating relation to oneanother whereby a crosspiece member in said first plurality is disposedbetween a pair of crosspiece members in said second plurality and viceversa, a third plurality of spaced crosspiece members disposed inparallel relation to one another and extending transversely to saidfirst and second pluralities of spaced crosspiece members between otherportions of said boundary member, said boundary member and said first,second and third pluralities of crosspiece members being integral withone another and being fabricated of the same material respectively insaid one piece element, said boundary member and said transverselydisposed crosspiece members defining therebetween a plurality of screenopenings, said boundary member being constructed to exhibit a bendingresistance that is different from the bending resistances of said first,second and third pluralities of crosspiece members, said first pluralityof crosspiece members being constructed to exhibit bending resistancesthat differ from the bending resistances of said second plurality ofcrosspiece members whereby two opposite sides of each of said screenopenings in said screen panel are defined respectively by a pair ofmembers whose bending resistances differ from one another, and aplurality of tongues integral with and extending outwardly from saidboundary member and from said first and second pluralities of crosspiecemembers, said tongues being spaced from and extending in directionsparallel to said third plurality of spaced crosspiece members, at leasttwo of said tongues being located in each of said screen openings andextending respectively toward one another from said boundary members andsaid first and second crosspiece members, the said two tongues in eachof said screen openings having free ends which are spaced from oneanother to define a slot therebetween.
 2. The screen panel of claim 1wherein said first and second crosspiece members respectively havecross-sectional shapes that differ from one another.
 3. The screen panelof claim 1 wherein the cross section of said boundary member is largerthan that of the crosspiece members in each of said first, second andthird pluralities of crosspiece members.
 4. The screen panel of claim 1wherein the crosspiece members in said first plurality of crosspiecemembers are provided with reinforcement means operative to give saidfirst crosspiece members a bending resistance that differs from thebending resistance of the said second crosspiece members.
 5. The screenpanel of claim 1 wherein said boundary member is rectangular inconfiguration, said first and second pluralities of crosspiece membersbeing disposed substantially parallel to two opposite sides of saidrectangular configuration, said third plurality of crosspiece membersbeing disposed substantially parallel to the other two opposite sides ofsaid rectangular configuration, the distance between said other twoopposite sides and the closest ones of said third plurality ofcrosspiece members being greater than the distance between each pair ofsaid second plurality of crosspiece members.
 6. The screen panel ofclaim 1 wherein said slot varies in width in a direction transverse tothe plane of said screen panel.
 7. The screen panel of claim 1 whereinsaid at least two tongues are tapered in a direction toward theirrespective free ends.